1. Field of the Invention
The present invention relates to a method of removing sheath from an electric wire in an intermediate region for production of harnesses and the like. More particularly, it relates to a method of forming the sheath with a split slit or longitudinal slit and a method of stripping the sheath in order to remove the sheath.
2. Description of the Prior Art
A large number of devices for stripping sheath from an electric wire in an intermediate region have been proposed in recent years. The process of sheath removal by the commonest device of this type is illustrated in FIGS. 9 to 12. The device comprises a pair of first cutters 2 (in FIG. 9) for cutting into the sheath of an electric wire 1 along the outer periphery, a pair of second cutters 3 (in FIG. 10) for forming the sheath of the wire 1 with split slits running longitudinally of the wire 1, and electric wire transfer means (not shown) for holding and transferring the wire 1 in a predetermined direction.
In a first stage of the process, the electric wire transfer means holds the wire 1 at a predetermined position. As shown in FIG. 9, the first cutters 2 cut into the sheath at one end of an intermediate strip region 1S of the wire 1 along the outer periphery to form a slit 4.
The electric wire transfer means transfers the wire 1, so that the points of the second cutters 3 are disposed to the position corresponding to one end of the intermediate strip region of the wire 1, as shown by the two-dot chain lines of FIG. 10. Subsequently, the second upper and lower cutters 3 move toward each other to thrust the points of the second cutters 3 into the sheath at one end of the intermediate strip region 1S.
With the points of the second cutters 3 remaining stuck in the sheath, the electric wire transfer means transfers the wire 1 longitudinally in the direction of the arrow P. Accordingly, the second cutters 3 relatively move to the other end of the intermediate strip region 1S, as shown by the solid lines of FIG. 10. With the movement, the sheath in the intermediate strip region 1S is formed with two split slits 5, upper and lower, from one end to the other end thereof (shown by hatching in FIGS. 10 and 11).
As shown in FIG. 11, the electric wire transfer means transfers the wire 1 back to the position of the first cutters 2. The first cutters 2 form another slit 4 along the outer periphery in the sheath at the other end of the intermediate strip region 1S.
After the formation of the slits 4 and the split slits 5 in this manner, the sheath in the intermediate strip region is stripped off in the following sheath stripping process:
With the first cutters 2 remaining stuck in the slit 4 formed at the other end, the electric wire transfer means transfers the wire 1 longitudinally in the direction of the arrow Q. The slit 4 at the other end of the intermediate strip region 1S is engaged with the first cutters 2. When the wire 1 is moved in the Q direction, the sheath in the intermediate strip region (or waste strip 7) is split along the split slits 5 and stripped from a core wire 6.
The sheath has been conventionally removed from the wire in the intermediate region in the above-mentioned method.
The conventional method, however, has problems described below.
Since the cutting depth of the second cutters 3 into the sheath of the wire 1 is slight, the abutment of the second cutters 3 against the sheath causes the elastic compression deformation of the sheath, as shown in FIG. 13. In some cases, the elastic compression deformation of the sheath prevents the second cutters 3 from cutting into the sheath. When the wire 1 is transferred with such insufficient cutting, the split slits 5 cannot be achieved which are formed by securely splitting the sheath from one end of the intermediate strip region 1S to the other end thereof. Some non-split portions are generated in the split slits 5 in the next process for stripping, and there arises a problem that the sheath in the intermediate strip region cannot be stripped.
In the sheath stripping process of the conventional method, when the wire 1 is transferred from the position shown in FIG. 11 in the Q direction, the waste strip 7 is split along the split slits 5 to be bent temporarily. At this time, an elastic restoring force is generated in the waste strip 7 against the pushing force of the first cutters 2. The problem is that the elastic restoring force causes the tip of the waste strip 7 to proceed between the cutters 2 and the core wire 6. In this state, satisfactory sheath stripping in the intermediate strip region cannot be expected. As shown in FIG. 14, for example, when the tip of the waste strip 7 proceeds between the upper cutter 2 and the core wire 6, the wire 1 is pushed relatively downward, whereby the core wire 6 is damaged by the lower cutter 2 or is cut off in some cases.